Means for photographically recording sound



May 3 9 R. HART v MEANS FOR PHOTOGRAPHICALLY RECORDING SOUND Filed April 9, 1925 In uen to?" Busae Hart,

A ttar/L eg.

Patented May 3, 1927.

UNITED STATES RUSSELL HART, OF LOS ANGEIiES, CALIFORNIA.

MEANS FOR PHOTOGBAPHICALLY RECORDING SOUND.

Application filed April 9, 1923. Serial No. 630,870.

M invention relates to means for photographically recording sound modulated light variations upon a moving sensitized film; and among my salient objects are, first, to

.provide a way for modifying the image of aconstant light source in such a manner that its total actinic value will always be proportionate to the corresponding ordinate of the sound wave being recorded; second, to secure virtual coincidence between the sound waves and the corresponding modified actinic values of the image; and, third, to afford facilities for continuously photographing the modified image in such a manner as to constitute a complete and undistorted record of the sound waves.

Other important objects are to supply a method for producing a sound record of great sharpness adapted, for example, for practically perfect reproduction of articus lated voice; and to accomplish the recording at a film speed corresponding to that commonly employed in the taking of motion pictures. I

Still further objects. and advantages of my invention will appear hereinafter, and while I show herewith and will describe. a preferred form of construction, I desire to be understood that I do not limit myself to such form, since various changes and adaptations may be made therein without departing from the spirit of the invention as hereinafter claimed.

It is well known that a true graphical representation of sound waves comprises a more or less complex curve in whichthe variation in value of the ordinates corresponds to variations in sound pressures. The position of the axis of abscissae has no eifect upon the shape' of the curve, and may be taken so that the curve is wholly above the axis. The area below such a curve, above the axis, may

then be considered as made up of an infinite number of vertical elementary strips of infinitesimal width, with no gaps or spaces between.

A similar area Willbe produced if we continuously photograph a luminous line, of varying length upon a film moving at a constant speed, provided the image of the line is parallel tothe film and perpendicular to the direction of its motion. Ifthe imageof such a line is extremely thin, and if its length is at all times proportional to. the corresponding ordinate of the above described curve, we shall have one margin of the photographed area bounded by a curve that trulyrepresents the sound wave. This photographed area, is adapted for reproduction of the original sound, by methods that have been developed.

The present invention concerns itself with means for photographically recording sound waves in the manner just described, and in the embodiment selected for illustrative purposes-as disclosed in thaaccompanying drawf i Figure 1 1's a sectional elevation of the complete device, the sectional plane corresponding in position to the line 1-1 of Fig. 2;

Figure 2 is a, sectional plan view of a portion of the apparatus taken on the line 2-'-2 of Fig. 1; showing details not included in the other figures of the drawing;

Figure 3 is a fragmentary interior elevation of the recording end of the apparatus taken on the line 33 of Fig. 1; V

Figure is an enlarged side view of a preferred form of light source having certain characteristicsthat particularly fit it for the purpose herein described;

Figure 5 is an enlarged elevation of the light modulating head, shown in central see tion;

Figure 6 is a much magnified diagrammatic view of the modulating shutter, or target; and

Figure 7 is a planview of a portion of a sound record made upon a motion picture film in accordance with my improved means.

Similar reference numerals refer to similar parts throughout the several views.

Before passing to a detailed description of my apparatus it should he understood that the present invention involves only a means for photographically recording sound waves. It does not concern itself with reproduction of the sound except to produce a record adapted for such reproduction by practical methods' that have been devised.

Referring to Fig. 1 of the drawing it will be noted that, in the form of my invention herein described, the apparatus is mostly contained within two elongated light-proof -box structures, or cameras, 8 and 9. The

first of these is used in a horizontal position and referably is fixedly mounted on a substantlal pedestal 10 in such location and manner as not to be subjected to the,efiects of external'mechanical vibrations. This is the light modulating portion of the appacurately positioned vertically and transversely thereon as by a pair of rails, one of which is shown at 12. The positioning is such that the longitudinal center lines of the two cameras intersect at right angles, and

the transverse center line of camera 9 C0111- cides with the longitudinal center line bf camera 8.

Microscopic focusing of both cameras is made prior to recording and thisis done in sequence. Camera 8 is focused first, with 9 slid back on the rails out of the way, or re moved from its step on the pedestal entirely After 8 is properly focused, 9 is careful y slid on the rails up against it, and the two cameras are then firmly bolted or latched together prior to the focusing of 9. One method of attaching the cameras together is by means of lugs as indicated in plan view at 13 in Fig. 2.

For the light source I employ a special tubular gas filled lamp L plainly illustrated in Fig. 4. This contains a single linear tungsten filament 14, of very small diameter and capable of being operated at a high temperature ,siThis filament is stretched be tween a longitudinal terminal 15 and a resilient transverse terminal 16, in such a manner as to be under spring tension at all times, so as to prevent its sagging when operated in a horizontal position. The maximum bending moment of terminal 16 occurs at the point where it is sealed into the glass tube of the lamp. This point is at a considerable distance from the hot filament, and

therefore not subjected to great temperature. Moreover the terminal may be a relatively wide flat st-ri having considerable radiating surface. For these reasons the terminal does not become annealed and it retainsits resiliency indefinitely. .This lam is mounted in a clamp 17 in the center 0 one'inside end of camera 8, in such a manner that the filament intersects the longitudinal axis of the camera at right angles, and may be adjusted to a horlzontal position. as .by the wing nut 18.

The modulating means I employ comprise a modulating head 19 and a diaphragm 20,

of ordinary acoustic construction, as illustrated in Fig. 5. They are used in such position that the diaphragm is horizontal. The

head is connected to a sound tube 21 and sound horn22 in any suitable manner, as

by the telescoping swivel joints illustrated.

In the center of the diaphragm is mounted a small stiff post 23, carrying a very small razor-edged target 24 at its upper extremity. Therazor edge 25 is either ground, or mounted, in a slight yjoblique'position as illustrated most clearly in the magnified fectly view of Fig. 6, and adjustment means 26 are provided for bringing the center of edge 25 in exact coincidence with the longitudinal axis of the camera. The sound waves, incoming through horn 22 and tube 21, impinge against the under surface of diaphragm 20, and the resulting vibration of the latter causes razor edge 25 to cut more or less deeply across the horizontal axial plane of the camera. The. oblique angular edge of the target permits a very small vertical movement of the latter to make a relatively great variation in the length of this cut.

Intermediate the light source and the modulating means is a lens arrangement 27 adapted for focusing in a convenient manner as by racks and pinions 28, and handwheel 29. This lens group is mounted coaxial with the camera.

The image of the light source, after the filament has beeen adjusted horizontally intersecting the camera axis, is focused upon razor edge 25 by means of the lens group 27. This is accomplished with great accuracy by means of a portable microscope 30, adapted for inserting in the fixed tube 31 which is mounted on the end of the camera for this purpose. The microscope is first focused on the razor edge, and then handwheel 29 is adjusted until the image of the light source appears sharp in the microscope without changing its focal adjustment.

Camera 9, as shown in Fig. 1, is partitioned horizontally in such a manner as to form reel boxes 32 at its upper and lower extremities. Access to these is had through side openin doors 33. The reel boxes communicate w1th the central chamber 34 only by means of small narrow slits 35 adapted for the passage of the photographic film strip 36. v

' For photogra hically recording sound the film strip must given a continuousl uniform motion, and I prefer to emp oy a synchronous motor for this purpose. The

' driving means must be positive in character,

and the film mustbe constrained to lie perflat'at the point where it is being exposed. It must also be-v prevented from chattering, or vibrating as the result of, friction.

I employ ordinary reels 37 for the film; any suitab e type of'feed sprockets 38, guide rollers 39, and pressure gate device 40. The feed sprockets are gear connected as shown at 41, and the driving power is applied to sprocket shaft 42 by means of the gear 43. The other-"sprocket shaft 44 carries a pulley 45, by means of which the take-up ree may be yieldingly driven.

' While being exposed, the film in the gate mechanism passes between two polished plates 46 and 47. These are pressed to-' gather by light helical springs surrounding the guide screw studs 48 in the manner com mon to the art. Flatness of field is positively attained in this way, the exposure being had through small apertures 49 in the plates in front of the film. Plate 47, be-

' for the purpose of transferring the modified image of the filament from razor edge 25 to the sensitized surface of the film strip.

Focusing of this lens group is accomplished by the rack and pinion movement 52.

I have devised a particularly delicate and satisfactory method for obtaining an accurate focus of the transferred image upon the sensitized surface of the film. For this purpose I first place a piece oi. exposed film etween plates 46 and 4'? and, after inserting the microscope in tube 50, I focus it carefully upon the metallic crystals in the exposed surface, as viewed from the rear through the aperture in plate 47 and the transparent material of the film. Ithen pull out the exposed film and move camera 9 to its operating position against camera 8, and

' adjust focusing screw 52 until the transferred image of the light source. appears sharp in the microscope; meanwhile allowing the vfocal adjustment of the microscope to remain undisturbed. The unrecorded film strip is then placed in the apparatus and recording can commence.

The main features of the construction and operation of my invention will be clearly apparent from the foregoing description, but it is desired to call especial attentlon to certain of the refining features that might otherwise be overlooked.

Chief among these refinements is the very delicate method of modulating the actinic value of the light image. By referring to the much magnified view of the target, as

' shown in Fig. 6,it willbe seen that a vertical movement equal in'total to the distance between arrow heads 53, serves to completely eclipse the full length of the image, which is indicated by 54. By reducing the angle of obliquity of. razor edge 25, a still smaller vertical movement of the target will serve to eclipse-the image. The angle of obliquity can easily be made adjustable if. desired, as by the screw 55 clamping the slotted end 56 of target post 23.

A second refinement is the possible demagnification of the luminous filament at the razor edge. If the diameter of the filament is in reality, say, one thousandth of i an inch, and the ratio of de-ma'gnification is one-to four, then the virtual diameter of the image will only be one-four-thousandth of an inch. This is so small that for practical purposes it closely approaches the width of the infinitesimal strips mentioned in the theoretical discussion of the subject in the early part of this specification.

Athird refinement comprises the methods of microscopic focusing. An image of the luminous filament is first very accurately focused in the plane of the razor edge, so that the point where the edge eclipses the light rays is very sharply defined. This primary image is then thrown as a secondary image upon the sensitized film, exactly focused in its plane, by the method described above. The resulting photographed record is much sharper than it would be possible to make it if the razor-edge merely intercepted the unfocused rays from the light source.

As previously pointed out, the sound record made in the manner described, and illustrated in Fig. 7, comprises a photographed area 57, bounded on one side by a complex Utl phragm; and details of arrangement and adjustment of parts; fall within the scope of my invention.

In a companion applicatlon, filed December'22. 1922, Serial Number 608,499, I disclosed certain features of construction herein shown but not claimed in this application.

I claim:

1. Apparatus of the character described,

comprising; a luminous rectilinear filament of great tenuity; a lens, for focusing an image of the filament in a plane; a target vibratile to sound in said plane 'for variably eclipsing the light rays forming said image to vary the length of the image; a

photo-sensitized surface, movable parallel to said plane; and a second lens for rojecting a seconda versely to its direction of motion.

2. Apparatus of the character described,

comprising; a luminous rectilinear filament of great tenuity, angularly adjustable about a transverse axis; a lens 'for focusing an image of the filament in a. plane; a tar et vibratile to sound in said. plane for varia 1y eclipsing' the light rays forming said image image of the varia le first 7 image upon t e sensitized surface, trans to modify the length of the image visible beyond said plane; a photo-sensitized surface, movable parallel to said plane; and a second lens for projecting a secondary image of the variable first image upon the sensitized surface, transversely to its direction of motion.

3. Apparatus of the character described, comprising; tenuity, angularly adjustable about a transverse axis; a lens for focusing an image of the filament in a plane; a target vibratile to sound in said plane for variably eclipsing the light rays forming said image to modify the length of the image visible beyond said plane; a photo-sensitized surface, movable parallel to said plane; and a second lens for projecting a secondary image of the variable first image upon-the sensitized surface transversely to its direction of motion; said target having a ray intercepting edge variably oblique to the first image.

t. The combination of a luminous rec-tilinear filament with; a lens adapted for foa luminous filament of great cusing an image of said filament in a plane; a target vibratile to sound in said plane having an edge obliquely intersecting said image; a photo-sensitized surface uniformly movable parallel to said plane and spaced therefrom; and a second lens intermediate the target and sensitized surface whereby a combined image of the target and filament image may be focused upon said sensitized surface.

5. The combination of rectilinear lumin0us filament of great tenuity with; means for focusing an image of the filament in a plane; means in said plane, vibratile to sound, for variably eclipsing the light rays to modify the length of said image visible beyond the plane; a photo-sensitized surface, movable parallel to said plane; and means for projecting a secondary image of said modified primary image upon said sensitized surface, transversely to its direction 4! of motion.

RUSSELL HART. 

